The Syrian regime has been accused of "extensive" use of cluster bombs over the last 18 months in a damning report by human rights activists.

Use of the weapons by forces loyal to President Bashar al-Assad amounted to indiscriminate targeting of civilians, and had left more than 165 people either dead or injured last year alone, the Human Rights Watch report said.

The Syrian death and in jury toll accounted for the overwhelming majority of the 190 documented cases worldwide caused by the banned weapons in 2012.

"Syria used cluster munitions extensively in the second half of 2012 and the first half of 2013, causing numerous civilian casualties," said the study, Cluster Munition Monitor Report.

The report, which is produced annually, measures how far countries have lived up to their responsibilities under international law in implementing the 2008 Convention on Cluster Munitions, which bans all use, production, transfer and stockpiling of the weapons.

"Syria is persisting in using cluster bombs - insidious weapons that remain on the ground, causing death and destruction for decades," said the report's editor, Mary Wareham.

"Syria's extensive use of cluster munitions has caused needless civilian casualties."

Wareham welcomed the international condemnation of the Syrian regime's use of the bombs, after 113 countries spoke out against their use.

"Other countries around the world that have joined the treaty are showing a strong commitment to get rid of cluster bombs once and for all," added Wareham, who is advocacy director of the organisation's Arms Division.

Unexploded bomblets

Cluster munitions can be fired by artillery, rocket launchers or aircraft. They typically explode in the air before impact, sending hundreds of unexploded "bomblets" over an area the size of a football pitch.

The bomblets often fail to explode on impact, leaving landmines littering the ground in the form of unexploded munitions.

The Netherlands, Denmark, France, Germany, Italy, Britain and others destroyed an unprecedented 173,973 cluster munitions over the 12-month period, the report said.

Seventeen countries, mainly in Asia and Europe, continue to produce the weapons or reserve the right to do so in the future, according to the report.

Only three nations which manufacture the bombs - the US, Russia and Israel - are known to have used them.

"Syria's extensive cluster munition use is casting a sombre shadow over the real progress that the convention is making to put an end to the human suffering that these weapons cause," Wareham said.

"Any US use of cluster munitions in Syria would only make the humanitarian crisis worse. It is crucial that all countries stigmatise cluster munitions by affirming these weapons should never be used."

The report was published ahead of a convention on the use of the weapons to be held in Zambia.

The Syrian regime has denied it possesses cluster bombs.